1. Field of the Invention
The present invention relates to an arm operation mechanism for moving a workpiece vertically and/or horizontally. The present invention also relates to an industrial robot including such an arm operation mechanism.
2. Description of the Related Art
A typical prior art industrial robot includes a plurality of arms pivotally connected to each other for vertically or horizontally moving a workpiece or processing tool held by one of the arms. Such a robot is often referred to as xe2x80x9carticulated robotxe2x80x9d. An example of articulated robot is disclosed in JP-A-2000-24966 for example. For the convenience of description, the articulated robot disclosed in this Japanese document is illustrated in FIG. 6 of the accompanying drawings.
As shown in FIG. 6, the prior art industrial robot includes a machine base 90, a first arm 91 having a base end and a tip end, a second arm 92 having a base end and a tip end, a first parallel link 94a, a second parallel link 94b, and a link base 95. The base end of the first arm 91 is pivotally supported on the machine base 90, whereas the base end of the second arm 92 is pivotally connected to the tip end of the first arm 91 via a coupler 93. The tip end of the second arm 92 is provided with a workpiece holder 96 for holding a workpiece (not shown). the workpiece holder 96 is integrally pivotable with a lever 97.
The first arm 91 is driven by a motor M1 for rotation about a fixed axis 97. The base end of the second arm 92 is provided with a gear 80a which is connected, via a shaft 81, to a gear 80b which is rotated by the motor M1. The opposite ends of the shaft 81 are provided with bevel gears 82a, 82b for meshing with the gears 80a, 80b, respectively.
One parallel link 94a is pivotally connected to the machine base 90 and to the link base 95, respectively. The other parallel link 94b is pivotally connected to the link base 95 and to the lever 97 of the workpiece holder 96.
With the above-described structure, when the first arm 91 is rotated about the axis 97 in the arrow Na directions, the second arm 92 rotates about the coupler 93 in the arrow Nb directions. Thus, the tip end of the second arm 92 and the workpiece holder 96 move up and down in the arrow Nc directions.
However, the above-described prior art robot has the following drawbacks. In the prior art robot, the rotational force of the gear 80b driven by the motor M1 is transmitted to the gear 80a via the shaft 81 for rotating the second arm 92 based on the rotation of the first arm 91. Therefore, the shaft 81 needs to be substantially equal, in length, to the first arm 91. Further, though not illustrated, the first arm 91 need be provided with a support mechanism, which may include a bearing for example, for supporting the shaft 81. Thus, the provision of the shaft 81 and the support mechanism in the arm 91 increases the size of the first arm 91, which leads to an increase in the overall size of the robot. Further, the provision of the shaft 81 and the support mechanism, which may be relatively large in weight, also increases the inertia of the first arm 91 during the rotation. Therefore, it may often be difficult to make the first arm 91 move quickly unless the motor M1 is high-powered.
It is an object of the present invention to provide an arm operation mechanism which operates suitably while having a simple structure and relatively small size and weight.
Another object of the present invention is to provide an industrial robot incorporating such an arm operation mechanism.
According to a first aspect of the present invention, there is provided an arm operation mechanism which comprises a support, a first arm, a second arm, a link base, a parallel link, and a conversion mechanism. The first arm has a tip end and a base end, and the base end of the first arm is pivotally connected to the support for rotation relative to the support. The second arm has a base end pivotally connected to the tip end of the first arm for rotation relative to the first arm. The link base is pivotally connected to the first arm for rotation relative to the first arm. The parallel link keeps a constant posture of the link base upon the rotation of the first arm. The conversion mechanism converts the rotation of the link base relative to the first arm into the rotation of the second arm relative to the link base.
Preferably, when the first arm rotates relative to the support in one direction through a first angle, the conversion mechanism causes the second arm to rotate relative to the first arm in an opposite direction through a second angle which is twice the first angle.
Preferably, the conversion mechanism comprises a first gear fixedly mounted to the link base, and a second gear rotatably mounted to the first arm in mesh with the first gear and operatively connected to the base end of the second arm.
Preferably, the conversion mechanism further comprises a third gear coaxial and integrally rotatable with the second gear, and a fourth gear fixedly connected to the second arm in mesh with the third gear. In this case, the fourth gear is fixedly connected to the base end of the second arm via a sleeve on which the first gear is coaxially and rotatably fitted. Further, the first gear and the second gear have a gear ratio of 1:1 while the third gear and the fourth gear have a gear ratio of 2:1. Moreover, the first arm may be hollow to accommodate all of the first through the fourth gears.
According to a second aspect of the present invention, there is provided an industrial robot comprising a holder and an arm operation mechanism for movably supporting the holder. The arm operation mechanism comprises a support, a first arm, a second arm, a link base, a parallel link, and a conversion mechanism. The first arm has a tip end and a base end, and the base end of the first arm is pivotally connected to the support for rotation relative to the support. The second arm has a base end pivotally connected to the tip end of the first arm for rotation relative to the first arm. The link base is pivotally connected to the first arm for rotation relative to the first arm. The parallel link keeps a constant posture of the link base upon the rotation of the first arm. The conversion mechanism converts the rotation of the link base relative to the first arm into the rotation of the second arm relative to the link base.
Preferably, the arm operation mechanism causes the tip end of the second arm to move vertically, and the holder includes a hand for supporting and moving a workpiece horizontally. The hand may be rotatable about a vertical axis. Further, the holder may also include a holder support pivotally connected to the tip end of the second arm, and the arm operation mechanism additionally includes a second parallel link pivotally connected to the link base and the holder support for constantly keeping the hand in a horizontal posture.
Other features and advantages of the present invention will become clearer from the detailed description given below with reference to the accompanying drawings.